Hello there! My name is Adam. I’ve read that someone hacked your customer's hosting account (yes, usually it's hacked account, not only single Wordpress site).
I'll clean this hosting account from malware. I'll also secure it - don't ask me how, it depends on what I'll find: it may be a vulnerable plugin, a weak password or anything else, there are dozens of possibilities.
I guarantee that this site stays clean from malware after this project ends - don't worry, I won't disappear, I take responsibility for my projects.
I am highly qualified for this project - I have a 3+ years experience cleaning and securing hacked websites/hosting accounts. Actually, I do it on daily basis as a freelancer (I'm a server admin in my full-time job). You may want to take a look at my feedbacks.
If you have any question, just drop me a message or let's discuss details on chat.
Best regards,
Adam